Collagen Structure
At present, nineteen types of collagens have been identified. These collagens, including fibrillar collagen types I, II, III, are synthesized as procollagen precursor molecules which contain amino- and carboxy-terminal peptide extensions. These peptide extensions, referred to generally as "pro-regions," are designated as N- and C-propeptides, respectively.
Both the N-propeptide and C-propeptide are typically cleaved upon secretion of the procollagen triple helical precursor molecule from the cell to yield a mature triple helical collagen molecule. Upon cleavage, the "mature" collagen molecule is then capable of associating into highly structured collagen fibers. See e.g., Fessler and Fessler, 1978, Annu. Rev. Biochem. 47:129-162; Bornstein and Traub, 1979, in: The Proteins (eds. Neurath, H. and Hill, R. H.), Academic Press, New York, pp. 412-632; Kivirikko et al., 1984, in: Extracellular Matrix Biochemistry (eds. Piez, K. A. and Reddi, A. H.), Elsevier Science Publishing Co., Inc., New York, pp. 83-118; Prockop and Kivirikko, 1984, N. Engl. J. Med. 311:376-383; Kuhn, 1987, in: Structure and Function of Collagen Types (eds. Mayne, R. and Burgeson, R. E.), Academic Press, Inc., Orlando, Fla., pp. 1-42.
Diseases Associated With The Abnormal Production of Collagen
An array of critical diseases has been associated with the inappropriate or unregulated production of collagen, including pathological fibrosis or scarring, including endocardial sclerosis, idiopathic interstitial fibrosis, interstitial pulmonary fibrosis, perimuscular fibrosis, Symmers' fibrosis, pericentral fibrosis, hepatitis, dermatofibroma, billary cirrhosis, alcoholic cirrhosis, acute pulmonary fibrosis, idiopathic pulmonary fibrosis, acute respiratory distress syndrome, kidney fibrosis/glomerulonephritis, kidney fibrosis/diabetic nephropathy, scleroderma/systemic, scleroderma/local, keloids, hypertrophic scars, severe joint adhesions/arthritis, myelofibrosis, corneal scarring, cystic fibrosis, muscular dystrophy (duchenne's), cardiac fibrosis, muscular fibrosis/retinal separation, esophageal stricture, payronles disease. Further fibrotic disorders may be induced or initiated by surgery, including scar revision/plastic surgeries, glaucoma, cataract fibrosis, corneal scarring, joint adhesions, graft vs. host disease, tendon surgery, nerve entrapment, dupuytren's contracture, OB/GYN adhesions/fibrosis, pelvic adhesions, peridural fibrosis, restenosis.
One strategy for the treatment of these diseases is the inhibition of the pathological overproduction of collagen. The identification and isolation of enzymes involved in the collagen production and processing are therefore of major medical interest to provide for suitable targets for drug development.
Similarly, a strategy for the treatment of diseases resulting from the pathological underproduction of collagen, where the underproduction of collagen is the consequence of improper processing of procollagen, is the administration of C-proteinase.
Background Information Regarding C-Proteinase
C-proteinase is an enzyme that catalyzes the cleavage of the C-propeptide of fibrillar collagens, including type I, type II, and type III collagen. The enzyme was first observed in culture media of human and mouse fibroblasts (Goldberg et al., 1975, Cell 4:45-50; Kessler and Goldberg, 1978, Anal. Biochem. 86:463-469), and chick tendon fibroblasts (Duskin et al., 1978, Arch. Biochem. Biophys. 185:326-332; Leung et al., 1979, J. Biol. Chem. 254:224-232). An acidic proteinase which removes the C-terminal propeptides from type I procollagen has also been identified. Davidson et al., 1979, Eur. J. Biochem. 100:551.
A partially purified protein having C-proteinase activity was obtained from chick calvaria in 1982. Njieha et al., 1982, Biochemistry 23:757-764. In 1985, natural C-proteinase was isolated, purified and characterized from conditioned media of chick embryo tendons. Hojima et al., 1985, J. Biol. Chem. 260:15996-16003. Murine C-proteinase has been subsequently purified from media of cultured mouse fibroblasts. Kessler et al., 1986, Collagen Relat. Res. 6:249-266; Kessler and Adar, 1989, Eur. J. Biochem. 186:115-121.
Experiments conducted with these purified forms of chick and mouse C-proteinase have indicated that the enzyme is instrumental in the formation of functional collagen fibers. Fertala et al., 1994, J. Biol. Chem. 269:11584.
Generally, C-proteinase activity and the inhibition of the enzyme's activity have been determined using a wide array of assays. See e.g., Kessler and Goldberg, 1978, Anal. Biochem. 86:463; Njieha et al., 1982, Biochemistry 21:757-764. As articulated in numerous publications, the enzyme is difficult to isolate by conventional biochemical means and neither the enzyme nor the cDNA sequence encoding such enzyme was known to be available prior to the instant invention. Takahara et al., 1994, J. Biol. Chem. 269:26280-26285, 26284 (C-proteinase's "peptide and nucleotide sequences are as yet unavailable"). Thus, despite the availability of C-proteinase related assays, large scale review and testing of potential C-proteinase inhibitors has not been performed to date.
Known C-Proteinase Inhibitors
A number of potential C-proteinase inhibitors have been identified. For example, several metal chelators have demonstrated activity as a C-proteinase inhibitor. Likewise, chymostatin and pepstatin A have been found to act as relatively strong inhibitors of C-proteinase activity.
.alpha..sub.2 -Macroglobulin, ovostatin, and fetal bovine serum appear to also, at least partially, inhibit C-proteinase activity. Similarly, dithiothreitol, SDS, concanavalin A, Zn.sup.2+, Cu.sup.2+, and Cd.sup.2+ possess inhibitory activity at low concentrations, and some reducing agents, several amino acids (including lysine and arginine), phosphate, and ammonium sulfate have been found to have C-proteinase inhibitory activity at concentrations of 1-10 mM. Leung et al., supra; Ryhanen et al., 1982, Arch. Biochem. Biophys. 215:230-236.
High concentrations of NaCl or Tris-HCl buffer have also been found to inhibit the C-proteinase activity. For example, it has been reported that 0.2, 0.3, and 0.5M NaCl reduces the activity of C-proteinase by 66, 38, and 25%, respectively, of that observed with the standard assay concentration of 0.15M. Tris-HCl buffer in a concentration of 0.2-0.5M likewise has been reported to inhibit the enzyme's activity. Hojima et al., supra.
In contrast, microbial inhibitors such as leupeptin, phosphoramidon, antipain, bestatin, elastinal, and amastatin, are considered to have weak or no effect.
Background Information Regarding Bone Morphogenic Protein-1 (BMP-1)
A protein having the structural characteristics of C-proteinase was isolated in 1988 from bone tissue. Prior to the instant invention, it was believed that this protein, designated BMP-1 or "bone morphogenic protein," was a member of the TGF-.beta. related protein family (Wozney et al., 1988, Science 242:1528-1534), as BMP-1 was isolated coincidentally with BMP-2A and BMP-3. Although evidence provides that BMP-2A and BMP-3 play a key role in the stimulation of bone development and growth, the activity of BMP-1 was never clearly established.
Sequence comparison reveals that BMP-1 contains a EGF-like domain and a region designated as "A-domain" having sequence similarity with a protease isolated from crayfish. Titany et al., 1987, Biochemistry 26:222. As the TGF-.beta.1 binding protein also contains EGF-like domains, it has been suggested that BMP-1 could be a protease involved in the activation of TGF-.beta.1. Miyazono et al., 1988, J. Biol. Chem. 263:6407; Woyznek et al., supra; Fukagawa et al., 1994, Dev. Bio. 162:175-183.
It has also been suggested that, due to homology to the Drosophila melanogaster tolloid gene product, BMP-1 is involved in the overall mechanism for the dorsal-ventral patterning of the neural tube.
While it has been suggested that C-proteinase ("for which [prior to this invention] peptide and nucleotide sequence are as yet unavailable") and BMP-1 belong to the same structural family, BMP-1 has never been associated with the formation of collagen. Takahara et al., 1994, J. Biol. Chem. 269:26280-26286. Thus, while a cDNA and polypeptide sequence of the putative bone morphogenic protein BMP-1 had been identified, no correct activity or use was known for this protein until the present invention. Similarly, the structural relationship between BMP-1 and C-proteinase was not known.